Golf ball compositions and method of making same

ABSTRACT

The present invention is directed to a golf ball and to a process for forming a golf ball having at least one layer, where the layer is formed of a saponified polymer/oxa acid blend, having from about 65 to about 99 parts of at least one saponified polymer and from about 35 to 1 parts of at least one oxa acid, based on 100 parts by weight of the saponified polymer/oxa acid blend. The layer may be foamed or unfoamed, and may form at least a portion of any of the cover, the core, or a mantle layer situated between the cover and the core.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.09/132,193, filed Aug. 10, 1998, now allowed, which is acontinuation-in-part of U.S. application Ser. No. 08/978,510, filed onNov. 25, 1997, now U.S. Pat. No. 5,869,578, which is a continuation ofU.S. application Ser. No. 08/560,763, filed on Nov. 21, 1995 (nowabandoned). Each of these applications is incorporated herein in itsentirety by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to golf balls and, in particular,to golf balls having at least one layer comprising a blend of at leastone saponified polymeric material and at least one oxa acid. Thesaponified polymeric material may be unmodified, or may contain at leastone pendant functional group that is grafted to the polymer chain. Thelayer, which may be foamed or unfoamed, may be located in any of thecover or core of the ball or in a mantle layer located between the coverand the core.

BACKGROUND OF THE INVENTION

[0003] Three-piece, wound golf balls with balata covers are preferred bymany expert golfers. These balls provide a combination of distance, highspin rate, and control that is not available with other types of golfballs. However, balata is easily damaged in normal play, and, thus,lacks the durability required by the average golfer.

[0004] In contrast, amateur golfers typically prefer a solid, two-pieceball with an ionomer cover, which provides a combination of distance anddurability. Because of the hard ionomer cover, these balls are almostimpossible to cut, but also have a very hard “feel”, which many golfersfind unacceptable, and a lower spin rate, making these balls moredifficult to draw or fade. The differences in the spin rate can beattributed to the differences in the composition and construction ofboth the cover and the core.

[0005] Many attempts have been made to produce a golf ball with thecontrol and feel of a wound balata ball and the durability of a solid,two-piece ball, but none have succeeded totally. In various attempts toproduce an ideal golf ball, the golfing industry has blended hardionomer resins (i.e., those ionomer resins having a hardness of about 60to 66 on the Shore D scale, as measured in accordance with ASTM methodD-2240) with a number of softer polymeric materials, such as softerpolyurethanes. However, the blends of the hard ionomer resins with thesofter polymeric materials have generally been unsatisfactory in thatthese balls exhibit numerous processing problems. In addition, the ballsproduced by such a combination are usually short on distance.

[0006] While different blend combinations of species of one variety ofpolymer, such as prior art ionomers, i.e., copolymers of an olefin andan α,β-unsaturated carboxylic acid, have been successfully used in theprior art, different polymers, such as carboxylic acid based ionomersand balata or other non-ionic polymers have not been successfullyblended for use in golf ball covers. In general, prior art blends ofpolymer components are immiscible, i.e., heterogeneous on a microscopicscale, and incompatible, i.e., heterogeneous on a macroscopic scale,unless strong interactions are present between the polymer components inthe mixture, such as those observed between carboxylic acid basedionomers and other polymers containing carboxylic acid groups. Inparticular, this lack of compatibility exists when an ionomer is blendedwith a polyolefin homopolymer, copolymer, or terpolymer that does notcontain ionic, acidic, basic, or other polar pendant groups, and is notproduced with a metallocene catalyst. These mixtures often have poortensile strength, impact strength, and the like. Hence, the golf ballsproduced from these incompatible mixtures will have inferior golf ballproperties such as poor durability, cut resistance, and so on. Incontrast, a compatible blend may be heterogeneous on a microscopicscale, but is homogeneous on a macroscopic scale, and, thus, has usefulgolf ball properties.

[0007] In this regard, U.S. Pat. No. 5,397,840 discloses golf ballcovers including a blend of “ionic copolymers” and “non-ioniccopolymers”. However, the “ionic copolymers” are defined as copolymersof an α-olefin and a metal salt of an α,β-unsaturated carboxylic acid,and the “non-ionic copolymers” are copolymers or terpolymers containingethylene or propylene and acrylic or methacrylic acid monomers.Therefore, strong interactions exist between the metal salts of the“ionic copolymers” and the acrylic or methacrylic acid monomers of the“non-ionic copolymers” that allow compatible blends to be formed. Theseinteractions do not exist in prior art blends of ionomers and polymersthat are truly non-ionic or nonpolar.

[0008] U.S. Pat. No. 5,616,640 to Harris et al. discloses golf ballcover compositions comprising an oxa acid compound having the formula

[0009] which may be blended with prior art, carboxylic acid basedionomers to provide golf balls having an excellent spin rate and goodshear resistance.

[0010] Co-pending application Ser. No. 08/978,510 discloses golf ballscomprising “saponified ionomers”, i.e., ester based ionomeric polymersproduced by carrying out a hydrolysis or saponification on copolymerscontaining pendant ester groups to form an ionomeric polymer that isless hydrophilic than typical carboxylic acid based ionomers to providegolf balls having enhanced physical properties when compared to priorart golf balls.

[0011] However, there is no known disclosure of golf balls comprisingcompatible blends of oxa acids and saponified ionomers.

[0012] Hydrolysis or saponification of alkyl acrylate units in acrosslinkable polymer chain is disclosed by Gross in U.S. Pat. No.3,926,891. This is accomplished by dissolving the polymer in an aqueousalkali metal hydroxide solution and then heating. The product isrecovered by coating the solution onto a substrate and evaporating thewater or by extruding the solution into a non-solvent. In U.S. Pat. No.3,970,626, Hurst discloses heating a mixture of an alkali metalhydroxide, a thermoplastic ethylene-alkyl acrylate copolymer and waterto saponify the acrylate units and form an aqueous emulsion. Thisemulsion can be used as such, partially dried to a paste or moist solid,or fully dried to solid form.

[0013] A different approach to hydrolysis or saponification of anethylene-alkyl acrylate copolymer is disclosed by Kurkov in U.S. Pat.No. 5,218,057, in which the copolymer is mixed with an aqueous solutionof an inorganic alkali metal base at a temperature sufficient forsaponification to take place and at which the copolymer undergoes aphase change. Typically, the copolymer would be molten when mixed withthe aqueous solution.

[0014] Each of these prior methods, with the exception of that disclosedin co-pending application Ser. No. 08/978,510, requires that the polymercomponent be in contact with water, either by conducting the reaction inan aqueous medium or by adding an aqueous solution to the polymer.Processes of this nature pose several disadvantages, however. First, itis difficult to remove water from the hydrolyzed or saponified polymerproduct. The polymer product is in the form of a salt that has a morepolar nature than the reactant acrylate ester, and so is more likely toassociate with or hydrogen bond to a polar solvent like water. Theenergy required to remove a highly interacting polar solvent like wateris much greater than for a nonpolar or weakly polar organic solvent.Second, it is important to remove water from the ionomer product becausethe presence of water can have detrimental effects on ionomer mechanicalproperties imparted by the polar ionic domains, which act as theeffective crosslink sites. Residual water weakens the ionic interactionswithin these domains, thereby reducing the mechanical property benefitsthe domains impart. Finally, incomplete removal of water can lead todifficulty in later fabricating steps where the product ionomer isreheated and shaped, e.g., into golf ball covers. Residual water cancause undesirable irregularities and imperfections on the surface offabricated articles by the formation of blisters. Residual water withinfabricated polymer articles can lead to void formation and evenuncontrolled foaming with a concomitant undesirable influence on themechanical properties, load bearing capacity and durability of thefabricated articles.

[0015] Melt state neutralization of an ethylene-acrylic acid copolymerby a solid, solution or slurry of an alkali metal salt is disclosed byWalter in U.S. Pat. No. 3,472,825. In the examples provided, hydrolysisis accomplished by mixing an alkali hydroxide with copolymer at constanttemperature either in a Banbury mixer or on a two roll mill. Walter doesnot disclose the use of extrusion type polymer processing apparatus forthis neutralization.

[0016] McClain, in U.S. Pat. No. 4,638,034, discloses a process wherebyethylene-acrylic acid copolymers or their ionomers are prepared fromethylene-alkyl acrylate copolymers by saponifying the latter in the meltwith metal hydroxides to form an ionomer and a by-product, i.e.,alkanol, then optionally acidifying the ionomer to form the free acidcopolymer. This process proceeds in the molten state and in the absenceof solvent or water, other than the by-product alkanol. Saponificationproceeds under non-static mixing conditions, typically with equipmentcommonly employed in the art of mixing molten polymer materials such asmultiroll mills, a Banbury mixer or a twin screw extruder.

[0017] The process disclosed by the '034 reference is, however,incapable of providing optimal product quality since blending andsaponifying in a single operation as taught by the subject referenceleads to rapid hydrolysis, with a concurrent rapid increase inviscosity. Due to this rapid increase in viscosity, the resultantmixture is non-uniform and therefore the physical properties of productsmade from this material are not consistent throughout the product.

[0018] During the melt state conversion of the alkyl-acrylate copolymerto the metal acrylate copolymer salt, a great decrease in melt flow rateoccurs with a corresponding great increase in melt viscosity. While notwishing to be bound by any particular theory, this decreased melt flowrate is thought to occur because of the tendency of the relatively polarionic salt functionalities formed during the saponification reaction toassociate with themselves rather than the relatively nonpolar unreactedalkyl acrylate or comonomer chain segments. Aggregations of saltmoieties arising from side groups attached to different chains intoionic domains introduces effective crosslink points throughout themolten copolymer. The effective crosslinks, in turn, greatly increasethe copolymer melt viscosity and, correspondingly, greatly decreasecopolymer melt flow rate.

[0019] A need exists in the golf ball art for highly durable golf balls,which have improved performance, and may be tailored to have virtuallyany combination of feel and spin rate. The present invention providessuch a golf ball.

SUMMARY OF THE INVENTION

[0020] The present invention is directed to a golf ball having least onelayer, where the layer is formed of a saponified polymer/oxa acid blend,comprising from about 65 to about 99 parts, preferably from about 75 toabout 99 parts, and most preferably from about 85 to about 99 parts ofat least one saponified polymer and from about 35 to 1 parts, preferablyfrom about 25 to about 1 parts, and most preferably from about 15 toabout 1 parts of at least one oxa acid, based on 100 parts by weight ofthe saponified polymer/oxa acid blend. The layer may be foamed orunfoamed, and may form at least a portion of any of the cover, the core,or a mantle layer or other intermediate layer situated between the coverand the core, where the core may be wound, solid, hollow, or filled witha fluid or a gel.

[0021] Preferred oxa acids include monoacids of formula:

[0022] and diacids of formula:

[0023] wherein n is an integer greater than or equal to 1, preferablyfrom 1 to 27, and R is typically H or CH₃, but may also be any organicmoiety selected from the group consisting of a linear or branch chainedalkyl, a substituted or unsubstituted carbocyclic or heterocyclicgroups.

[0024] The saponified polymer typically comprises a first olefinic,monomeric component having from 2 to 8 carbon atoms and a secondmonomeric component comprising an unsaturated carboxylic acid basedacrylate class ester having from 4 to 22 carbon atoms and at least oneester group, wherein at least a portion of the ester groups have beensaponified with an inorganic metal base. Useful inorganic metal basesinclude, but are not limited to metal bases comprising at least onemetallic cation, such as lithium, sodium, potassium, cesium, magnesium,calcium, barium, manganese, copper, zinc, titanium, tungsten, zirconium,and aluminum, and at least one anion, such as hydroxide, alkoxide,acetate, carbonate, bicarbonate, oxide, formate, and nitrate.

[0025] Typically, the first monomeric component is an α-olefin monomerhaving a terminal point of unsaturation, and may be of the formula:

[0026] where R₁ is hydrogen or an alkyl group, and R₂ is hydrogen, loweralkyl including C₁-C₅, carbocyclic, aromatic or heterocyclic.Preferably, the first monomeric component is ethylene.

[0027] Typically, the first monomeric component comprises from about 1to about 99 percent by weight of the total polymer weight, preferablyfrom about 10 to about 95 percent by weight of the total polymer weight,and most preferably from about 10 to about 70 percent by weight of thetotal polymer weight.

[0028] The second monomeric component is typically an unsaturatedacrylate class ester having the formula:

[0029] where R₃ is hydrogen or an alkyl group; R₄ is hydrogen, loweralkyl including C₁-C₅, carbocyclic, aromatic or heterocyclic; R₅ isselected from the group consisting of C_(n)H_(2n+1), for n=1 to 18 andphenyl, in which from 0 to 5 H within R₄ can be replaced by substituentsselected from the group consisting of COOH, SO₃H, NH₂, succinicanhydride and their salts, F, Cl, Br, I, OH, SH, epoxy, silicone, loweralkyl esters, lower alkyl ethers, and aromatic or heterocyclic ringswith the proviso that R₄ and R₅ can be combined to form a bicyclic ring.Typically, the second monomeric component comprises from about 99 toabout 1 percent by weight of the total polymer weight, preferably, fromabout 90 to about 5 percent by weight of the total polymer weight, andmost preferably, from about 90 to about 30 percent by weight of thetotal polymer weight.

[0030] The saponified polymer may also comprise a third monomericcomponent. Useful third monomeric components include carbon monoxide,sulfur dioxide, an anhydride monomer, an unsaturated monocarboxylicacid, an olefin having from 2 to 8 carbon atoms and a vinyl ester or avinyl ether of an alkyl acid having from 4 to 21 carbon atoms. Preferredthird monomeric components include monomers of formula:

[0031] wherein:

[0032] R₆ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic;

[0033] R₇ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic;

[0034] R₈ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic;

[0035] R₉ is hydrogen or lower alkyl including C₁-C₅;

[0036] R₁₀ is hydrogen, or is selected from the group consisting ofC_(n)H_(2n+1), for n=1 to 18 and phenyl, in which from 0 to 5 H withinR₁₀ can be replaced by substituents selected from the group consistingof COOH, SO₃H, NH₂ and their salts, F, Cl, Br, I, OH, SH, silicon, loweralkyl esters, lower alkyl ethers and aromatic or heterocyclic rings withthe proviso that R₉ and R₁₀ can be combined to form a bicyclic ring;

[0037] R₁₁ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic;

[0038] R₁₂ is hydrogen or lower alkyl including C₁-C₅;

[0039] R₁₃ is hydrogen, or is selected from the group consisting ofC_(n)H_(2n+1), for n=1 to 18 and phenyl, in which from 0 to 5 H withinR₁₃ can be replaced by substituents selected from the group consistingof COOH, SO₃H, NH₂ and their salts, F, Cl, Br, I, OH, SH, epoxy,silicon, lower alkyl esters, lower alkyl ethers and aromatic orheterocyclic rings with the proviso that R₁₂ and R₁₃ can be combined toform a bicyclic ring.

[0040] Typically, the third monomeric component comprises from about 0to 49 percent by weight of the total polymer weight of the saponifiedpolymer. The monomeric components of the polymer may be present in arandom, alternating, block or graft arrangement, and the saponifiedpolymers may be isotactic, syndiotactic, atactic polymers, or acombination thereof.

[0041] A grafting agent may also be added to the saponified polymer toform a grafted polymer. The preferred grafting agent is an anhydridehaving the formula:

[0042] where R₁₄ and R₁₅ are the same or different, and are typicallyhydrogen, linear or branched chain alkyl, or substituted orunsubstituted carboxylic groups.

[0043] The grafting agent is typically added in an amount of betweenabout 1 to about 50 percent by weight, preferably from about 1 to about25 percent by weight, and most preferably from about 1 to about 15percent by weight of the polymer.

[0044] The present invention is also directed to a process for forming agolf ball. The method of the invention comprises blending a saponifiedpolymer with at least one oxa acid to form a saponified polymer/oxa acidblend; and forming at least one layer of a golf ball from the saponifiedpolymer/oxa acid blend.

[0045] Preferably, the method of the invention further comprises forminga polymer comprising a first olefinic monomeric component having from 2to 8 carbon atoms and a second monomeric component comprising anunsaturated carboxylic acid based acrylate class ester having from 4 to22 carbon atoms; applying a sufficient amount of heat to the polymer toconvert the polymer to a substantially molten state; forming a mixtureby adding an inorganic metal base to the molten polymer; saponifying themixture to form a saponified polymer, where a sufficient amount of theinorganic metal base is added to the molten polymer in forming themixture to obtain a degree of saponification of the polymer rangingbetween about 1 and 50 percent. Most preferably the mixture of theinorganic metal base and the molten polymer is formed at a temperatureat which the viscosity of the mixture remains substantially unchangedfrom the viscosity of the molten polymer Optionally, the polymer furthercomprises a third monomeric component, such as carbon monoxide, sulfurdioxide, an anhydride monomer, an unsaturated monocarboxylic acid, anolefin having from 2 to 8 carbon atoms, or a vinyl ester or a vinylether of an alkyl acid having from 4 to 21 carbon atoms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 is a cross-sectional view of a two-piece golf ballaccording to the invention with a one-piece core.

[0047] FIG. 2 is a cross-sectional view of a golf ball according to theinvention incorporating a multi-layer core.

[0048] FIG. 3 is a cross-sectional view of a golf ball according to theinvention incorporating a mantle layer between the cover and the core.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] As used herein, the terms “saponified polymer” and “saponifiedionomer” refer to a polymer comprising at least one olefin and at leastone unsaturated monomer that contains a pendant ester group, where atleast some of the pendant ester groups have been hydrolyzed orsaponified. Saponified ionomers differ from prior art ionomers in thatany pendant groups that are not modified by the saponification processare ester groups in contrast to the pendant carboxylic acid groups thatremain after neutralization in prior art ionomers.

[0050] The terms “saponified polymer/oxa acid blend” and “saponified/oxaacid blend”, as used herein, refers to any polymer blend that comprisesat least one saponified polymer and at least one oxa acid.

[0051] As used herein, the term “layer” includes any generally sphericalportion of a golf ball or golf ball core, center, or mantle, includingone-piece cores and one-piece balls. A “mantle” or other intermediatelayer is defined herein as a portion of the golf ball that occupies avolume between the cover and the core. Of course, as one of ordinaryskill in the art would recognize, any of the core, cover, and mantle ofthe golf balls of the invention can be formed of one layer or aplurality of layers, as that term is defined herein.

[0052] As used herein, the term “metallocene catalyzed polymer” refersto any polymer, copolymer, or terpolymer, and, in particular, anypolyolefin, polymerized using a metallocene catalyst. The term “graftedmetallocene catalyzed polymer” refers to any metallocene catalyzedpolymer in which the metallocene catalyzed polymer has been subjected toa post-polymerization reaction to graft at least one functional grouponto the metallocene catalyzed polymer. Similarly, the term “non-graftedmetallocene catalyzed polymer” refers to any metallocene catalyzedpolymer in which the metallocene catalyzed polymer has not beensubjected to such a post-polymerization reaction. Accordingly, the term“metallocene catalyzed polymer” encompasses both non-grafted metallocenecatalyzed polymers and grafted metallocene catalyzed polymers.

[0053] The present invention relates to golf balls including at leastone foamed or unfoamed layer that comprises a blend of at least onesaponified polymer and at least one oxa acid, i.e., a saponifiedpolymer/oxa acid blend. As noted above, the layer may be in any of thecore, the cover, or a mantle layer situated between the cover and thecore.

[0054] Golf balls of the invention comprising saponified polymer/oxaacid blends useful in the invention comprise at least one layer of ablend of at least one oxa acid and at least one saponified polymer,comprising from about 65 to about 99 parts, preferably from about 75 toabout 99 parts, and most preferably from about 85 to about 99 parts ofat least one saponified polymer and from about 35 to 1 parts, preferablyfrom about 25 to about 1 parts, and most preferably from about 15 toabout 1 parts of at least one oxa acid, based on 100 parts by weight ofthe saponified polymer/oxa acid blend. Typically, the layer has athickness of from about 0.005 to about 0.125 inch and a Shore D hardnessof from about 15 to about 80. Where the layer is foamed, the polymerblends may be foamed during molding by any conventional foaming orblowing agent. Preferably, foamed layers incorporating a saponifiedpolymer/oxa acid blend have a flexural modulus of from about 1000 toabout 150,000 psi.

[0055] Saponified polymer/oxa acid blends in accordance with theinvention, comprising at least one saponified polymer and at least oneoxa acid, may be thermoformed, and, thus, can be either compression orinjection molded to form a layer of foamed or unfoamed saponifiedpolymer/oxa acid blend in the cover, core, or mantle of a golf ballaccording to the invention. Blends of oxa acids and saponified polymersare resilient, easily processed materials that allow highly durable golfballs to be produced with improved performance and virtually anycombination of feel and spin rate.

[0056] Golf balls according to the invention may incorporate corescomprising saponified polymer/oxa acid blends, as well as saponifiedpolymers or polymer blends, grafted metallocene catalyzed polymers orpolymer blends, non-grafted metallocene catalyzed polymers or polymerblends, or conventional materials, such as poly-butadiene. Corescomprising a blend of at least one saponified polymer and at least oneoxa acid may be either one-piece, comprising a single piece of foamed orunfoamed saponified polymer/oxa acid blend, or multi-piece, comprising aliquid or solid core or center and one or more layers in which any ofthe center or at least one of the layers comprises a foamed or unfoamedblend of a saponified polymer and an oxa acid.

[0057] For example, FIG. 1 illustrates a golf ball according to theinvention with a one-piece core. Golf ball 1 comprises a core 2 and acover 3, wherein either of core 2 or cover 3 incorporates at least onelayer comprising a foamed or unfoamed blend of a saponified polymer andan oxa acid.

[0058] Similarly, FIG. 2 illustrates a golf ball according to theinvention incorporating a multi-piece core. Golf ball 10 comprises acover 12, a core having a center 14 and at least one additional corelayer 16. Any of the cover 12, center 14, or core layer 16 mayincorporate at least one foamed or unfoamed layer that comprises asaponified polymer/oxa acid blend.

[0059] Conventional materials useful in centers, cores, or core layersof the golf balls of the invention include, but are not limited to,compositions having a base rubber, a crosslinking agent, and a filler.The base rubber typically includes natural or synthetic rubbers. Apreferred base rubber is 1,4-polybutadiene having a cis-structure of atleast 40 percent. Natural rubber, polyisoprene rubber and/orstyrene-butadiene rubber may be optionally added to the1,4-polybutadiene. Crosslinking agents include metal salts ofunsaturated fatty acids, such as zinc or magnesium salts of acrylic ormethacrylic acid. The filler typically includes materials such as zincoxide, barium sulfate, silica, calcium carbonate, zinc carbonate and thelike. Golf balls of the invention may also have conventional woundcores, where the core comprises a liquid or solid center wrapped inelastomeric windings.

[0060] Golf balls of the invention may also include a mantle layer orother intermediate layer situated between the cover and the core.Preferably, the mantle layer comprises a least one foamed or unfoamedlayer that comprises a saponified polymer/oxa acid blend, but may alsobe formed from a saponified polymer or polymer blend, a grafted ornon-grafted metallocene catalyzed polymer or polymer blend, or from anyother suitable polymeric material having the desired properties,including, but not limited to, block copolymers of a poly(ether-ester),such as HYTREL®, available from DuPont, block copolymers of apoly(ether-amide), such as PEBAX®, available from Elf Atochem,styrene-butadiene-styrene and styrene-(ethylene-propylene)-styrene orstyrene-(ethylene-butylene)-styrene block copolymers, and theirfunctionalized derivatives, such as KRATON D®, KRATON G®, and KRATON FG®from Shell Chemical.

[0061] A golf ball incorporating a mantle layer is illustrated in FIG.3, which depicts golf ball 20, having cover 23, core 24, and a mantlelayer 25 situated between the cover and the core. Any of cover 23, core24, and mantle layer 25 may incorporate at least one layer of a foamedor unfoamed saponified polymer/oxa acid blend. Moreover, core 24 may bea one-piece core, a multi-layer core, or a wound core, having a solid orliquid center.

[0062] Golf balls according to the invention may also incorporate coverlayers comprising foamed or unfoamed saponified polymer/oxa acid blends,grafted metallocene catalyzed polymers or polymer blends, non-graftedmetallocene catalyzed polymers or polymer blends, blends of saponifiedpolymers, oxa acids, and metallocene catalyzed polymers or conventionalmaterials, including balata and ionomer cover stock. Saponifiedpolymer/oxa acid blend cover layers according to the invention may beused with conventional solid or wound cores, as well as those comprisingsaponified polymers or grafted or non-grafted metallocene catalyzedpolymers or polymer blends. Preferably, the cover of a golf ballaccording to the invention is formed from a blend comprising at leastone saponified polymer and at least one oxa acid.

[0063] The use of a foamed saponified polymer/oxa acid blend also allowsthe golf ball designer to vary the density or mass distribution of theball to adjust the angular moment of inertia, and, thus, the spin rateand performance of the ball. Foamed materials also offer a potentialcost savings due to the reduced use of polymeric material.

[0064] As used herein with regard to saponified polymers and oxa acids,the phrase “branched or straight chain alkyl” means any substituted orunsubstituted acyclic carbon-containing compounds. Examples of alkylgroups include lower alkyl, for example, methyl, ethyl, n-propyl,iso-propyl, n-butyl, iso-butyl or tert-butyl; upper alkyl, for example,octyl, nonyl, decyl, and the like; and lower alkylene, for example,ethylene, propylene, butylene, pentene, hexene, heptene, octene,norbornene, nonene, decene and the like. The ordinary skilled artisan isfamiliar with numerous linear and branched alkyl groups, which arewithin the scope of the present invention.

[0065] In addition, such alkyl groups may also contain varioussubstituents in which one or more hydrogen atoms has been replaced by afunctional group. Functional groups include, but are not limited tohydroxyl, amino, carboxyl, sulfonic amide, ester, ether, phosphates,thiol, nitro, silane and halogen (fluorine, chlorine, bromine andiodine), to mention but a few.

[0066] As used herein, “substituted and unsubstituted carbocyclic” meanscyclic carbon-containing compounds, including, but not limited tocyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and the like. Suchcyclic groups may also contain various substituents in which one or morehydrogen atoms has been replaced by a functional group. Such functionalgroups include those described above, and lower alkyl groups having from1-28 carbon atoms. The cyclic groups of the invention may furthercomprise a heteroatom.

[0067] As used herein, “substituted and unsubstituted aryl groups”refers to any functional group comprising a hydrocarbon ring having asystem of conjugated double bonds, such as phenyl, naphthyl, anisyl,toluyl, xylenyl and the like. According to the present invention, arylalso includes heteroaryl groups, e.g., pyrimidine or thiophene. Thesearyl groups may also be substituted with any number of a variety offunctional groups. In addition to the functional groups described abovein connection with substituted alkyl groups and carbocyclic groups,functional groups on the aryl groups can include nitro groups.

[0068] As used herein, “heterocyclic groups” means closed cycliccarbon-containing compounds wherein one or more of the atoms in the ringis an element other than carbon, e.g. sulfur, nitrogen, etc, includingbut not limited to pyridine, pyrrole, furan, thiophene, and purine.

[0069] As used herein, the term “polymer” means any type of polymerincluding random polymers, block polymers, etc.

Saponified Polymers and Polymer Blends

[0070] Saponified polymers useful in the invention can be made frompolymers of formula I:

[0071] wherein:

[0072] R₁ is hydrogen, alkyl such as methyl, ethyl, and branched orstraight chain propyl, butyl, pentyl, hexyl, heptyl, and octyl;

[0073] R₂ is hydrogen, lower alkyl including C₁-C₅ carbocyclic, aromaticor heterocyclic;

[0074] R₃ is hydrogen, alkyl such as methyl, ethyl and branched orstraight chain propyl, butyl, pentyl, hexyl, heptyl and octyl;

[0075] R₄ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic;

[0076] R₅ is selected from the group consisting of C_(n)H_(2n+1), forn=1 to 18 (which includes, for example, CH₃, C₂H₅, C₃H₇, C₄H₉, C₅H₁₁,C₆H₁₃, C₇H₁₅, C₉H₁₉, C₁₀H₂₁) and phenyl, in which from 0 to 5 H withinR₅ can be replaced by substituents selected from the group consisting ofCOOH, SO₃H, NH₂, succinic anhydride and their salts, F, Cl, Br, I, OH,SH, epoxy, silicone, lower alkyl esters, lower alkyl ethers, andaromatic or heterocyclic rings, with the proviso that R₄ and R₅ can becombined to form a bicyclic ring;

[0077] R₆ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic;

[0078] R₇ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic; and

[0079] wherein a, b and c are the relative percentages of eachco-monomer. Saponified polymers can also be formed from polymers offormula II:

[0080] wherein:

[0081] R₁, R₂, R₃, R₄, and R₅ are as defined above; and wherein d, e andf are the relative percentages of each co-monomer;

[0082] from polymers of formula III:

[0083] wherein:

[0084] R₁, R₂, R₃, R₄, and R₅ are as defined above; and wherein g, h,and i are the relative percentages of each co-monomer;

[0085] and from polymers of formula IV:

[0086] wherein:

[0087] R₁, R₂, R₃, R₄, and R₅ are as defined above; R₈ is hydrogen,lower alkyl including C₁-C₅, carbocyclic, aromatic or heterocyclic; R₉is hydrogen or lower alkyl including C₁-C₅; and R₁₀ is hydrogen, or isselected from the group consisting of C_(n)H_(2n+1), for n=1 to 18 andphenyl, in which from 0 to 5 H within R₁₀ can be replaced bysubstituents selected from the group consisting of COOH, SO₃H, NH₂,succinic anhydride and their salts, F, Cl, Br, I, OH, SH, epoxy,silicon, lower alkyl esters, lower alkyl ethers and aromatic orheterocyclic rings, with the proviso that R₉ and R₁₀ can be combined toform a bicyclic ring; and wherein k, m and n are the relativepercentages of each co-monomer.

[0088] In addition, saponified polymers can be formed from polymers offormula V:

[0089] wherein:

[0090] R₁-R₅ are as defined above; R₁₁ is hydrogen, lower alkylincluding C₁-C₅, carbocyclic, aromatic or heterocyclic; R₁₂ is hydrogenor lower alkyl including C₁-C₅; and R₁₃ is hydrogen or is selected fromthe group consisting of C_(n)H_(2n+1) for n=1 to 18 and phenyl, in whichfrom 0 to 5 H within R₁₃ can be replaced by substituents selected fromthe group consisting of COOH, SO₃H, NH₂, succinic anhydride and theirsalts, F, Cl, Br, I, OH, SH, epoxy, silicone, lower alkyl esters, loweralkyl ethers and aromatic or heterocyclic rings; and R₁₃ is the same asR₁₀, with the proviso that R₁₂ and R₁₃ can be combined to form abicyclic ring; and wherein r, s and t are the relative percentages ofeach co-monomer.

[0091] In each of the polymers described above, R₁ and R₂ can be anycombination of alkyl, carbocyclic or aromatic groups, for example,1-cyclohexylpropyl, benzyl cyclohexylmethyl, 2-cyclohexylpropyl,2,2-methylcyclohexylpropyl, 2,2-methylphenylpropyl,2,2-methylphenylbutyl. Comonomer units according to the above formulaeare easily manufactured according to techniques and synthetic strategieswell known to the skilled artisan. These comonomers are alsocommercially available from a number of commercial sources.

[0092] Saponified polymers can be random, block or alternating polymersand may be made by blending two, three, four, five or more differentmonomers according to processes well known to one of ordinary skill inthe art. Additionally, the subject polymers may be isotactic,syndiotactic or atactic, or any combination of these forms of types ofpolymers. The pendant groups creating the isotactic, syndiotactic oratactic polymers can be chosen to determine the interactions between thedifferent polymer chains making up the resin to control the finalproperties of the resins used in golf ball covers. Aromatic and cyclicolefins can be used in the present invention as well as such specificgroups as methyl and phenyl.

[0093] The comonomers described herein can be combined in a variety ofways to provide a final copolymer with a variety of characteristics. Theletters a, d, g, k, and r represent numbers that can independently rangefrom 1-99 percent, preferably from 10-95 percent, more preferably from10-70 percent and, most preferably, from about 10-50 percent. Thecoefficients b, e, h, m and s can independently range from 99-1 percent,preferably from 90-5 percent, more preferably from 90-30 percent, andmost preferred from 90-50 percent, and c, f, i, n and t canindependently range from 0 to 49 percent.

[0094] Graft copolymers of the saponified polymers described above canalso be prepared for use in forming golf balls. For example, graftpolymers can be produced such that the graft segment making up thelinkage between polymer chains comprises an anhydride, wherein“anhydride” is taken to mean a compound having the formula:

[0095] wherein:

[0096] R₁₄ and R₁₅ are the same or different and are chosen from amonghydrogen, linear or branched chain alkyl and substituted orunsubstituted carboxylic groups. Alternately, however, other graftingagents containing double or triple bonds can be used. Examples of thesematerials include, but are not limited to, acrylates, styrene andbutadiene.

[0097] Grafting the polymer molecules of the present invention can beaccomplished according to any technique known in the art. See, e.g.,Block and Graft Copolymers, by R. Ceresa, pub. by Butterworths, London,U.S. (1962), incorporated by reference herein. It is preferred that anygrafting of the polymers of the present invention be accomplished byadding from about 1 to about 50 percent, or preferably from about 1 toabout 25 percent and most preferably from about 1 to about 15 percent ofa grafting agent, such as an anhydride according to the formula above.The grafting agents can be added either as a solid or a non-aqueousliquid, to a polymer according to the present invention. Such postreaction grafting can make the final grafted polymer more flexible.

[0098] Polymers that can be saponified for use in the present inventioncan be synthesized by a variety of methods, including metallocenecatalysis, since it is well known in the art of polymer synthesis thatmany different synthetic protocols can be used to prepare a givencompound. Different routes can involve more or less expensive reagents,easier or more difficult separation or purification procedures,straightforward or cumbersome scale-up, and higher or lower yield. Theskilled synthetic polymer chemist knows well how to balance thecompeting characteristics of synthetic strategies. Thus, the saponifiedpolymers useful in the present invention are not limited by the choiceof synthetic strategy, and any synthetic strategy that yields thesaponified polymers described above can be used.

[0099] Polymers useful for saponification preferably comprise: (1) afirst monomeric component comprising an olefinic monomer having from 2to 8 carbon atoms; (2) a second monomeric component comprising anunsaturated carboxylic acid based acrylate class ester having from 4 to22 carbon atoms; and (3) an optional third monomeric componentcomprising at least one monomer selected from the group consisting ofcarbon monoxide, sulfur dioxide, an anhydride monomer, an unsaturatedmonocarboxylic acid, an olefin having from 2 to 8 carbon atoms and avinyl ester or a vinyl ether of an alkyl acid having from 4 to 21 carbonatoms.

[0100] Saponified polymers are preferably prepared by adding a metalbase or metal salt in the form of a solid or a solution to a polymer,such as the polymers described in the previous paragraph. Preferably,however, the metal base is in the form of a solid, such as a powder or apellet. Powdered bases used in the invention preferably have an averagepowder particle diameter of from about 1 to 500 microns. Morepreferably, such powders have an average particle diameter of 10 to 100microns. In the case of pellets, substantially any commerciallyavailable pellet particle size can be used.

[0101] Alternately, the metal base can be added in the form of asolution. Preferably, the solution is non-aqueous so that difficultiesarising from incomplete removal of water during subsequent processingand use are avoided. Such non-aqueous solutions typically comprisesolvents such as alcohol, acetic acid and acetic anhydride, althoughother solvents may, of course, be used.

[0102] The metal base comprises at least one metallic cation, such aslithium, Li, sodium, Na, potassium, K, cesium, Cs, magnesium, Mg,calcium, Ca, barium, Ba, zinc, Zn, manganese, Mn, copper, Cu, aluminum,Al, and at least one anion, such as hydroxide, alkoxide, acetate,carbonate, bicarbonate, oxide, formate, or nitrate.

[0103] The polymers described herein are preferably saponified orhydrolyzed by introducing the polymer into an extruder inlet zone, andmelting and mixing the polymer in the inlet zone; passing the moltenpolymer through an addition zone within the extruder downstream from theinlet zone; and adding a metal base into the molten polymer as it passesthrough the addition zone. The base may be added to the molten polymerunder saponification conditions until the polymer is at least partiallysaponified, as indicated by, for example, its melt index or by titratingversus an acid.

[0104] However, the metal base is preferably mixed with the polymerunder non-saponification conditions. Instead of simultaneously mixingand saponifying or hydrolyzing as practiced in the prior art, theseoperations are carried out separately. In the first step, the polymer isheated to a substantially molten state at a temperature typicallybetween about 50-350° C., depending upon the polymer chosen, tofacilitate subsequent mixing with a metal base. This pre-heating stepassures a greater degree of homogeneity in the final product, andprovides a final product having correspondingly improved properties.

[0105] In the next step, the metal base is added to the molten polymer,and the polymer and metal base are extensively mixed under conditions inwhich no substantial hydrolysis occurs. A sufficient amount of metalbase must be added overall to obtain a degree of saponification of thepolymer between about 1 and about 50 percent. The mixing is carried outat a temperature slightly higher than the melting temperature of thepolymer. For mixing on an extruder, the screw speed can be variedbetween about 20-500 rpm, depending upon the material's viscosity, i.e.,the higher the viscosity, the greater the screw rpm required.Furthermore, as would be well understood by one of ordinary skill in theart, the depth of the conveying element of the extruder is chosen toprevent substantial hydrolysis of the material during mixing.

[0106] Alternately, the mixing may be accomplished using a roll mill. Insuch a case, the cylinder roll speed is adjusted to between about 5-100rpm depending upon the viscosity of the material. Additionally, the millgap is adjusted as necessary to control the amount of shear, and thusthe degree of hydrolysis. The metal base may be added all at once to themolten polymer, or alternately it may be introduced in batches orstages.

[0107] In a third step, conditions are provided such that a hydrolysisor saponification reaction occurs between the polymer and the metalbase. Saponification is achieved by continuous mixing of the polymer andbase at an elevated temperature, which is substantially higher than themelting point temperature.

[0108] This novel process offers several improvements over the methodsdisclosed in the prior art. First, it provides for greater ease ofmixing of the reactants before the reaction begins. Because the meltviscosity of the non-salt polymer is much lower than the salt polymerform, the melt mixing of the polymer and metal base is more readilycarried out with lower input power requirements. Additionally, mixing ofpolymer and metal base is more uniform because there are nosubstantially hydrolyzed or saponified regions of low melt flow or highmelt viscosity present within regions that have not yet reacted and,therefore, have high melt flow and low melt viscosity. Furthermore, thedegree of mixing or dispersion of the base in the polymer is more easilycontrolled since melt flow rate is more uniform throughout the volume ofmolten polymer.

[0109] Once substantial saponification begins, the reaction is thoughtto be more uniform than the methods disclosed in the prior art. Althoughnot wishing to be bound by any particular theory, the controlleddispersion of reactants in the mixing phase is thought to result in amore uniform melt morphology during the hydrolysis phase. The greaterability to control mixing and its uniformity provided by the multi-stepprocess of this invention are thought to allow a finer morphologicaltexture to develop as the hydrolysis reaction proceeds. That is, smallersize regions arise from dissimilar polarities of the polymer salt formedfrom hydrolysis and the relatively less polar nonreacted regions andcomonomers. Additionally, the morphological texture that forms is notdisrupted by excessive shear mixing. With reduced variation in the sizeor extent of high and low melt flow rate regions, the melt hydrolysisproduct is thought to be more uniform in postsolidification morphologyand properties.

[0110] This process is preferably accomplished using a twin screwextruder wherein the twin screw extruder comprises melting, addition,and mixing zone means. The process can further be accomplished using amaster batch comprising a concentrated amount of metal base in apolymer, with the same or different composition as the polymerintroduced into the inlet zone, wherein the master batch is added from aside-stream extruder. The side-stream extruder can be a twin screwextruder comprising melting, addition, and mixing zone means.

[0111] Alternatively, the continuous process of saponifying orhydrolyzing the polymers useful in the invention comprises introducingthe polymer into an inlet zone of an extruder, and melting and mixingthe polymer in the inlet zone; passing the molten polymer through atleast two addition zones connected in series; and adding a portion of ametal base into the molten polymer as it passes through each additionzone until the polymer is at least partially saponified.

[0112] This process can be accomplished using a twin screw extruderwherein the twin screw extruder comprises melting, addition, and mixingzone means. The process can further be accomplished using a single or aplurality of master batches comprising a concentrated amount of metalbase in a polymer, with the same or different composition as the polymerintroduced into the inlet zone, and with the same or different amount ofmetal base as the other master batches, wherein the master batch isadded from a side-stream extruder. The process can be accomplished witha single or with multiple side-stream extruders which are twin screwextruders comprising melting, addition, and mixing zone means.

[0113] For use in saponified polymer/oxa acid blends of the presentinvention, a saponified polymer with ionomeric character can be blendedwith the other similar polymers, having a different metal base cation ordistribution of cationic species than used to make the first saponifiedpolymer, to yield a blend with desirable golf ball properties.Alternatively, two different saponified polymers with ionomericcharacter, having the same metal base cation can be blended to yield auseful blend. The two polymers can differ in their degree of hydrolysis,degree of subsequent acidification, molecular weight, molecular weightdistribution, tacticity, blockiness, etc.

Oxa Acids

[0114] Oxa acids useful in the invention include monoacids of theformula:

[0115] and diacids of formula:

[0116] wherein n is an integer greater than or equal to 1, preferablyfrom 1 to 27, and R is typically H or CH₃, but may be any organic moietyselected from the group consisting of a linear or branch chained alkyl,a substituted or unsubstituted carbocyclic or heterocyclic groups.

[0117] Any number of oxa acid compounds are contemplated as being usefulin the present invention. Some specific oxa acids useful in the novelgolf ball compositions of the present invention include3,6-dioxaheptanoic acid having the formula:

[0118] 3,6,9 trioxadecanoic acid, having the formula:

[0119] 3,6,9-trioxaundecanedioic acid, having the formula:

[0120] and Polyglycol diacid, having the formula:

[0121] Oxa acid compositions possess a variety of properties that makethem useful in the present golf ball compositions. These propertiesinclude wide liquid ranges due to their low melting and high boilingpoints, high viscosity, good heat stability, solubility in media ofwidely differing polarity, development of surface-active properties, andgood complexing properties for metal ions. This allows oxa acids toreadily blend with saponified polymers to form the saponifiedpolymer/oxa acid blends of the invention. In addition, oxa acidcompositions are useful as comonomers in a number of resin compositionsfor positively influencing a variety of properties of the resultingpolymers. Admixing oxa acids as a comonomer in the formation ofpolyesters, polyamides, polyurethanes and epoxy resins influencesproperties such as elasticity to avoid or eliminate cracking, viscosityand thixotropy, heat and light resistance, dyeability, static charging,mechanical resistance, wettability, initiation of polymerization, andmolecular weight.

[0122] Numerous oxa acid compounds useful in the cover compositions ofthe present invention are available from Hoechst Celanese Corporation,Fine Chemicals Division under the trade name “Oxa Acids.” See HoechstCelanese Corporation's “Oxa Acids” Brochure (1994).

[0123] Additionally, the oxa acid compounds can be synthesized by avariety of synthetic routes known to the skilled organic chemist. It iswell known in the art of organic synthesis that many different syntheticprotocols can be used to prepare a given compound. Different routes caninvolve more or less expensive reagents, easier or more difficultseparation or purification procedures, straightforward or cumbersomescale-up, and higher or lower yield. The skilled synthetic organicchemist knows well how to balance the competing characteristics ofsynthetic strategies. Thus the compounds of the present invention arenot limited by the choice of synthetic strategy, and any syntheticstrategy that yields the compounds described above can be used.

Saponified Polymer/Oxa Acid Blends

[0124] The saponified polymer/oxa acid blends of the present inventionmay be used alone or blended with other polymers or ionomers, accordingto methods well known in the art, to form compositions useful forforming golf balls.

[0125] For example, the saponified polymer/oxa acid blends of thepresent invention may be combined with thermoplastic ionomers, such asethylene methacrylic acid ionomers and ethylene acrylic acid ionomersand their terpolymers, which are sold commercially under the trade namesSURLYN® and IOTEK® by DuPont and Exxon respectively.

[0126] More preferably, the other polymers that can be used inconjunction with saponified polymer/oxa acid blends in golf ball coversinclude: block copolymers of a poly(ether-ester), such as HYTREL®available from DuPont, block copolymers of a poly(ether-amide), such asPEBAX® available from Elf Atochem, styrene-butadiene-styrene blockcopolymers, such as the KRATON D® grades available from Shell Chemical,styrene-(ethylene-propylene)-styrene orstyrene-(ethylene-butylene)-styrene block copolymers, such as the KRATONG® series from Shell Chemical, either of the KRATON®s with maleicanhydride or sulfonic graft or functionality, such as the KRATON FD® orKRATON FG® series available from Shell Chemical, olefinic copolymers,such as the ethylene-acrylate or ethylene methacrylate series availablefrom Quantum, metallocene catalyzed polymers, including ethylene-octenecopolymers made from metallocene catalysts, available as the AFFINITY®or ENGAGE® series from Dow, and ethylene-alpha olefin copolymers andterpolymers made from metallocene catalysts, available as the EXACT®series from Exxon, block poly(urethane-ester) or blockpoly(urethane-ether) or block poly(urethane-caprolactone), such as theESTANE series available from BF Goodrich, polyethylene glycol, such asCARBOWAX available from Union Carbide, polycaprolactone,polycaprolactam, polyesters, such as EKTAR available from Eastman,polyamides, such as nylon 6 or nylon 6,6, available from DuPont and ICI,ethylene-propylene-(diene monomer) terpolymers and their sulfonated orcarboxylated derivatives, and PP/EPDM and dynamically vulcanizedrubbers, such as SANTOPRENE from Monsanto.

[0127] The saponified polymer/oxa acid blends of the present inventioncan be prepared with or without the addition of a compatibilizer, andwith varying molecular architecture of blend components, such as varyingmolecular weight, tacticity, degrees of blockiness, etc., as is wellknown to those knowledgeable in the art of blending polymers.

[0128] The amounts of polymers used in the present invention can varyfrom 1 to 99 parts of the saponified polymer/oxa acid blend to 99 to 1parts of other polymers or ionomers, based on the total weight ofpolymers. More preferred ratios of 95 to 5 parts of the saponifiedpolymer/oxa acid blend with 5 to 95 parts of one or more other polymers.Most preferred is from about 95 to about 10 parts of the subjectsaponified polymer/oxa acid blends and from about 5 to about 90 parts ofthe other polymer or ionomer.

[0129] Blending of the saponified polymer/oxa acid blends isaccomplished in a conventional manner using conventional equipment. Goodresults have been obtained by mixing the resins in a solid, pelletizedform and then placing the mix into a hopper which is used to feed theheated barrel of the injection molding machine. Further mixing isaccomplished by a screw in the heated barrel. The injection moldingmachine is used either to make preformed half-shells for compressionmolding about a core or for molding flowable cover stock about a coreusing a retractable-pin mold. Such machines are conventional.

[0130] Additional components which can be added to the golf ballcompositions of the present invention include U.V. stabilizers, reactiveand non-reactive fillers, white pigments, e.g., TiO₂, ZnO, and BaSO₄,mica, talc, nano-fillers, colored pigments, fluorescent pigments,optical brighteners, light stabilizers, and metals, such as titanium,zinc, and tungsten.

[0131] The present polymers may be blended with any of the additionalingredients noted above, for example, to be used in a golf ball coverusing any conventional blending technique. For example, the presentcompounds may be added to a vessel containing pelletized polymer resinsand heated to 300 to 500° F. Thorough mixing of the materials isaccomplished by means of a screw in the heated vessel.

[0132] The saponified polymer/oxa acid blends of the invention can beused to form any type of golf ball. In particular, two-piece golf ballscomprising a cover surrounding a core are within the scope of thepresent invention, as are wound golf balls, in which a liquid,semi-solid or solid core is surrounded by an elastic synthetic material.The term “solid cores” as used herein refers not only to one piece coresbut also to those cores having a separate solid layer beneath the coverand above the core, and other multilayer and/or non-wound cores. Anytype of golf ball core can be used in the golf balls of the presentinvention. Preferred cores, however, include some amount ofcis-butadiene. The subject polymers may also be used in golf ballshaving multiple covers and/or multiple cores.

[0133] Typically, the covers are formed around the solid or wound coresby either compression molding preformed half-shells of the cover stockmaterial or by injection molding the cover stock about the core.Half-shells are made by injection molding a cover stock into aconventional half-shell mold in a conventional manner. The preferredmethod is compression molding of preformed half-shells.

[0134] In compression molding, the half-shells of the stock material areformed by injection molding the cover stock material, typically at 300°F. to 520° F., into a conventional half-shell mold for a short time. Thepreformed half-shells are then placed about a core and the assembly isintroduced into a compression molding machine, and compression moldedabout a core, typically at about 250 to 500° F. The compression moldingmachine is a hydraulic press having an upper and lower mold plate, whichhave half molds, each of which is registered with another half mold inthe opposite mold plate. The molded balls are then cooled while still inthe mold, and finally removed when the cover is hard enough to behandled without deforming.

[0135] Alternatively, golf balls can be covered solely with the use ofan injection molding technique. In injection molding, an injectionmolding machine is utilized in which the core assembly is placed in amold cavity. The core assembly is held in place through the use ofseveral retractable pins. Such injection molding machines are well knownin the art. The molten cover material is injected into the cavitysurrounding the core. As the cover material cools and hardens, the pinsretract and the molded ball is ejected from the mold. The balls thenundergo conventional finishing operations such as buffing, painting andstamping. This type of cover construction is generally referred to as aone-piece cover.

[0136] The present invention can be used in forming golf balls of anydesired size. While “The Rules of Golf” by the USGA dictates that thesize of a competition golf ball be no less than 1.680 inches indiameter, golf balls of any size can be used for leisure golf play.Therefore, while the preferred diameter of the golf balls is from about1.680 inches to about 1.800 inches, golf balls of any size are withinthe scope of the present invention.

[0137] While it is apparent that the invention disclosed herein is wellcalculated to fulfill the objects stated above, it will be appreciatedthat numerous modifications and embodiments may be devised by thoseskilled in the art. Therefore, it is intended that the appended claimscover all such modifications and embodiments that fall within the truespirit and scope of the present invention.

What is claimed is:
 1. A golf ball comprising a core and at least onecover layer formed of a saponified polymer/oxa acid blend, comprisingfrom about 65 to about 99 parts of at least one saponified polymer andfrom about 35 to 1 parts of at least one oxa acid, based on 100 parts byweight of the saponified polymer/oxa acid blend.
 2. The golf ballaccording to claim 1, wherein at least a portion of the core alsocomprises a saponified polymer/oxa acid blend.
 3. The golf ballaccording to claim 1, wherein the core is selected from the groupconsisting of wound cores, solid cores, hollow cores, cores filled witha fluid, and cores filled with a gel.
 4. The golf ball according toclaim 1, further a mantle situated between the cover and the core. 5.The golf ball according to claim 4, wherein the core is a wound core. 6.The golf ball according to claim 5, wherein at least a portion of themantle also comprises a saponified polymer/oxa acid blend.
 7. The golfball according to claim 1, wherein the oxa acid is a monoacid of theformula:

wherein n is an integer greater than or equal to 1, and R is H or anorganic moiety selected from the group consisting of linear and branchchained alkyl, substituted and unsubstituted carbocyclic, andheterocyclic groups.
 8. The golf ball according to claim 1, wherein theoxa acid is a diacid of the formula:

wherein n is an integer greater than or equal to
 1. 9. The golf ballaccording to claim 1, wherein the saponified polymer comprises a firstolefinic, monomeric component having from 2 to 8 carbon atoms and asecond monomeric component comprising an unsaturated carboxylic acidbased acrylate class ester having from 4 to 22 carbon atoms and at leastone ester group, wherein at least a portion of the ester groups havebeen saponified with an inorganic metal base.
 10. The golf ballaccording to claim 9, wherein the metal base comprises at least onemetallic cation, selected from the group consisting of lithium, sodium,potassium, cesium, magnesium, calcium, barium, manganese, copper, zinc,titanium, tungsten, zirconium, and aluminum, and at least one anion,selected from the group consisting of hydroxide, alkoxide, acetate,carbonate, bicarbonate, oxide, formate, and nitrate.
 11. The golf ballaccording to claim 9, wherein the first monomeric component comprises an_(α)-olefin monomer having a terminal point of unsaturation.
 12. Thegolf ball according to claim 11, wherein the first monomeric componenthas the formula:

wherein: R₁ is hydrogen or an alkyl group; and R₂ is hydrogen, loweralkyl including C₁-C₅, carbocyclic, aromatic or heterocyclic.
 13. Thegolf ball according to claim 12, wherein the first monomeric componentis ethylene.
 14. The golf ball according to claim 9, wherein the firstmonomeric component comprises from about 1 to about 99 percent by weightof the total polymer weight.
 15. The golf ball according to claim 9,wherein the first monomeric component comprises from about 10 to about95 percent by weight of the total polymer weight.
 16. The golf ballaccording to claim 9, wherein the first monomeric component comprisesfrom about 10 to about 70 percent by weight of the total polymer weight.17. The golf ball according to claim 8, wherein the second monomericcomponent is an unsaturated acrylate class ester having the formula:

wherein: R₃ is hydrogen or an alkyl group; R₄ is hydrogen, lower alkylincluding C₁-C₅, carbocyclic, aromatic or heterocyclic; R₅ is selectedfrom the group consisting of C_(n)H_(2n−1), for n=1 to 18 and phenyl, inwhich from 0 to 5 H within R₄ can be replaced by substituents selectedfrom the group consisting of COOH, SO₃H, NH₂, succinic anhydride andtheir salts, F, Cl, Br, I, OH, SH, epoxy, silicone, lower alkyl esters,lower alkyl ethers, and aromatic or heterocyclic rings with the provisothat R₄ and R₅ can be combined to form a bicyclic ring.
 18. The golfball according to claim 17, wherein the second monomeric componentcomprises from about 99 to about 1 percent by weight of the totalpolymer weight.
 19. The golf ball according to claim 17, wherein thesecond monomeric component comprises from about 90 to about 5 percent byweight of the total polymer weight.
 20. The golf ball according to claim17, wherein the second monomeric component comprises from about 90 toabout 30 percent by weight of the total polymer weight.
 21. The golfball according to claim 8, further comprising a third monomericcomponent selected from the group consisting of carbon monoxide, sulfurdioxide, an anhydride monomer, an unsaturated monocarboxylic acid, anolefin having from 2 to 8 carbon atoms and a vinyl ester or a vinylether of an alkyl acid having from 4 to 21 carbon atoms.
 22. The golfball according to claim 21, wherein the third monomeric component is atleast one of the monomers selected from the group consisting of:

wherein: R₆ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic; R₇ is hydrogen, lower alkyl including C₁-C₅,carbocyclic, aromatic or heterocyclic; R₈ is hydrogen, lower alkylincluding C₁-C₅, carbocyclic, aromatic or heterocyclic; R₉ is hydrogenor lower alkyl including C₁-C₅; R₁₀ is hydrogen, or is selected from thegroup consisting of C_(n)H_(2n+1), for n=1 to 18 and phenyl, in whichfrom 0 to 5 H within R₁₀ can be replaced by substituents selected fromthe group consisting of COOH, SO₃H, NH₂ and their salts, F, Cl, Br, I,OH, SH, silicon, lower alkyl esters, lower alkyl ethers and aromatic orheterocyclic rings with the proviso that R₉ and R₁₀ can be combined toform a bicyclic ring; R₁₁ is hydrogen, lower alkyl including C₁-C₅,carbocyclic, aromatic or heterocyclic; R₁₂ is hydrogen or lower alkylincluding C₁-C₅; R₁₃ is hydrogen, or is selected from the groupconsisting of C_(n)H_(2n+1), for n=1 to 18 and phenyl, in which from 0to 5 H within R₁₃ can be replaced by substituents selected from thegroup consisting of COOH, SO₃H, NH₂ and their salts, F, Cl, Br, I, OH,SH, silicon, lower alkyl esters, lower alkyl ethers and aromatic orheterocyclic rings with the proviso that R₁₂ and R₁₃ can be combined toform a bicyclic ring.
 23. The golf ball according to claim 21, whereinthe third monomeric component comprises up to about 49 percent by weightof the total polymer weight.
 24. The golf ball according to claim 9,wherein the monomeric components of the polymer are present in a random,alternating, block or graft arrangement.
 25. The golf ball according toclaim 9, wherein the polymer is isotactic, syndiotactic, atactic, or acombination thereof.
 26. The golf ball according to claim 1, wherein agrafting agent has been added to the saponified polymer to form agrafted polymer.
 27. The golf ball according to claim 26, wherein thegrafting agent comprises an anhydride having the formula:

wherein: R₁₄ and R₁₅ are the same or different and are selected from thegroup consisting of hydrogen, linear or branched chain alkyl andsubstituted or unsubstituted carboxylic groups.
 28. The golf ballaccording to claim 26, wherein the grafting agent is added in an amountof between about 1 and 50 percent by weight of the polymer.
 29. The golfball according to claim 26, wherein the grafting agent is added in anamount of between about 1 and 25 percent by weight of the polymer. 30.The golf ball according to claim 26, wherein the grafting agent is addedin an amount of between about 1 and 15 percent by weight of the polymer.31. A golf ball comprising a cover and a core and a mantle situatedbetween the cover and the core, wherein at least the core comprises atleast one layer formed of a saponified polymer/oxa acid blend comprisingfrom about 65 to about 99 parts of at least one saponified polymer andfrom about 35 to 1 parts of at least one oxa acid, based on 100 parts ofthe saponified polymer/oxa acid blend.
 32. The golf ball according toclaim 31, wherein the core is selected from the group consisting ofwound cores, solid cores, hollow cores, cores filled with a fluid, andcores filled with a gel.
 33. The golf ball according to claim 32,wherein the saponified polymer comprises a first olefinic, monomericcomponent having from 2 to 8 carbon atoms and a second monomericcomponent comprising an unsaturated carboxylic acid based acrylate classester having from 4 to 22 carbon atoms and at least one ester group,wherein at least a portion of the ester groups have been saponified withan inorganic metal base.
 34. The golf ball according to claim 31,wherein the oxa acids is a monoacid of the formula:

wherein n is an integer greater than or equal to 1, and R is H or anorganic moiety selected from the group consisting of linear and branchchained alkyl, substituted and unsubstituted carbocyclic, andheterocyclic groups.
 35. The golf ball according to claim 31, whereinthe oxa acid is a diacid of the formula:

wherein n is an integer greater than or equal to
 1. 36. The golf ballaccording to claim 31, wherein the at least one layer further comprisesat least one polymeric composition selected from the group consisting ofgrafted metallocene catalyzed polymers, grafted metallocene catalyzedpolymer blends, non-grafted metallocene catalyzed polymers, non-graftedmetallocene catalyzed polymer blends, balata, and ionomers.
 37. Aprocess for forming a golf ball, which golf ball comprises a cover, acore, and optionally a mantle situated between the cover and the core,which process comprises: blending a saponified polymer with at least oneoxa acid to form a saponified polymer/oxa acid blend; and forming atleast one layer of a golf ball cover from the saponified polymer/oxaacid blend.
 38. The process according to claim 37, further comprising:forming a polymer comprising a first olefinic monomeric component havingfrom 2 to 8 carbon atoms and a second monomeric component comprising anunsaturated carboxylic acid based acrylate class ester having from 4 to22 carbon atoms; applying a sufficient amount of heat to the polymer toconvert the polymer to a substantially molten state; forming a mixtureby adding an inorganic metal base to the molten polymer; and saponifyingthe mixture to form a saponified polymer, wherein a sufficient amount ofthe inorganic metal base is added to the molten polymer in forming themixture to obtain a degree of saponification of the polymer rangingbetween about 1 and 50 percent.
 39. The process according to claim 38,further comprising forming the mixture of the inorganic metal base andthe molten polymer at a temperature such that the mixture has aviscosity that remains substantially unchanged from that of the moltenpolymer.
 40. The process according to claim 38, further comprisingforming the polymer with a third monomeric component, selected from thegroup consisting of carbon monoxide, sulfur dioxide, an anhydridemonomer, an unsaturated monocarboxylic acid, an olefin having from 2 to8 carbon atoms, and a vinyl ester or a vinyl ether of an alkyl acidhaving from 4 to 21 carbon atoms.